Even though he's not so much unlikable as he is annoying, my vote goes to Kronk. I mean yes his stupidity is only for effect, but why can't Yzma just hire a smart henchman to actually get stuff done?
Villains hire stupid henchmen because
smart henchmen tend to try to usurp them. Look at Starscream. While not particularly bright, he tends to have a
lot more foresight than Megatron, and doesn't let him forget it. Starscream actually
revels in Megatron's failures and calls him out on it. Not to mention how the smart henchmen of Skelletor are constantly planning to get rid of him behind his back. Bungling henchmen may screw up, but when they screw up a plot that was bound to fail, at
least the main villain can come out and blame
everyone else for his imbecilic schemes.
Plus, it's totally implied that Yzma employs hot young men for
obvious reasons. Remember the line "This year's model is named Kronk." Implies that there were many other young, brawny men before him.